In order to cut precise double-sided boards, we need to install the alignment bracket. This comes with the machine and is secured to the edge of the spoilboard with three screws. I suggest installing the alignment bracket before securing the material. Once installed, in the BantamTools software, click on the Locate button near the fixturing option in the configure sidebar. The software will walk you through the process. It'll prompt you to flip your current milling tool so the blunt end can probe the spoilboard. Once installed it'll proceed to move the toolhead and probe the edges of the alignment bracket and set various offsets. This is how the software maps out where the material is relative to the alignment bracket. This procedure takes about 2-3minutes. Once finished, you can flip the end mill back and click Change under the tool section so the toolhead can probe the reinstalled tool by touching the spoilboard and automatically setting the z-axis offset. Once this is all setup, leave the alignment bracket on until the very end.
Use double-sided scotch tape to secure the FR-1 board to the spoilboard. I use the wide version, which covers more surface area. I use three long strips, evenly placed across the length of the board on the far top, bottom and middle section of the board. Do not overlap the strips or use too much as it will become difficult to remove. Since we're doing double-sided FR-1, doesn't matter which side you choose first. You'll want to wipe down the FR-1 board and the spoilboard with isopropyl alcohol with a paper towel. This will get rid of any debris, grease or finger prints from the surface.
When you're ready to install the material onto the spoilboard, carefully position the FR-1 board over the lower left corner of the alignment bracket. Square off the edges of the corner so they're both as flush as humanly possible. Then, press down on the material. I like to use a piece of paper towel over the material and apply an even amount of pressure so all of the tape adheres to the spoilboard.
Remember, we only want to mill the traces for the top layer and save the holes and outline for the bottom layer. Before milling, run through this checklist to ensure we're properly setup.
- Check the right milling tool is selected and configured – 1/32 end mill
- Check the right material profile is setup – Double-sided FR-1 Standard size
- Check the placement is set to the "left"
- Check each .brd part is milling only traces and NOT holes and outlines
- Check tightness of alignment bracket, toolhead and acrylic panels are properly shut
With everything checked and ready to mill, click the Mill All Visible button. The toolhead will start up and cut around the traces only and work its way through copies, if any. Be sure to watch as the operation takes place. You'll want to be aware and cautious in case something comes loose.
Once the top layer is done, you'll want to use a vacuum to clean out all of the dust and debris from inside the machine. I find it helpful to cycle between the Origin and Loading movements in the Move To section of BantamTools software. These are a quick way to move the toolhead and spoilboard out of the way so you can vacuum under the bed.
Inspect the traces and see if there's any rough edges. I recommend using a scotch brite pad to remove burrs. I spend a few minutes light buffing the surface. This knocks away most of the rough edges and burrs. I normally do this while the PCB is still secured to the spoilboard.
Next we'll need to remove the PCB from the spoilboard without damaging it. You can use a thin narrow spatula to pry off the PCB but it may lead to bending the FR-1. Use alcohol to soften the adhesive. I like to use a squeeze bottle (or narrow mouth wash bottle) to apply alcohol near the edges of the board. Then use the spatula to fit in between the FR-1 and spoilboard. Getting in between the strips of tape makes for easier removal. Be careful not to mar the bottom copper surface, so take it slow!
Inspect the bottom layer, slight marks can be buffed away with Scotch Brite pad. Proceed if all good. Apply strips of double-stick tape, this time to the top surface with the traces. Flip the board so the traces are facing the spoilboard and line it up with the lower right corner of the alignment bracket. Square the edges so they're as flush as possible. Apply pressure to whole board to fully adhere to the spoilboard.
In the software we'll need to turn on the holes and outline for each .brd file. Then, switch to the bottom side of the board by clicking the right alignment button. This will automatically flip each .brd file to the bottom side. Once ready to start cutting, hit the Mill All Visible button. The toolhead will start with the traces, move onto drilling holes and finally cutting the board outline – That takes a few passes to cut.
Once done you'll want to spend time vacuuming inside the machine using the same method as before. There's a bit more dust from the outlines and holes. Use a scotch brite pad again to buff out any burrs or rough edges.
Follow the process as before to remove the PCB from the spoilboard, again using alcohol and thin spatula. Inspect the top slide and remove any tape and excess FR-1. I recommend doing that over a waste bin to catch and debris and dust. Use scotch bright accordingly!